Shortly after the discovery of the opioid receptor in 1973, it became apparent that multiple opioid receptor subtypes (mu, delta, kappa and ORL-1) existed based on pharmacological, biochemical, anatomical and ultimately molecular evidence. Highly-specific and selective opioid receptor subtype agonists for the mu (e.g. DAMGO), delta-1 (e.g., DPDPE), delta-2 (e.g., deltorphin), kappa (e.g., U50488H) and ORL-1 (e.g., orphanin FQ-nociceptin) and antagonists for the mu (e.g., beta-funaltrexamine, CTOP), mu-1 (e.g., naloxonazine), delta (e.g., naltrindole) and kappa (e.g., nor-binaltorphamine) were developed and used by our laboratory and others to characterize which opioid receptor subtypes were involved in spontaneous intake and body weight gain in normal, developing, dietarily-obese and genetically-obese animals, in such regulatory challenges as food and water deprivation, glucoprivation and lipoprivation, in such stress-related issues as tail pinch feeding, and in such hedonic situations utilizing concentrations of sugars (e.g., sucrose), fats and starches (e.g., maltose dextrin). The orosensory characteristics of opioid function were studied using the sham-feeding paradigm minimizing post-ingestive factors.

Opioid Receptor Subtype and Feeding Publications of the Bodnar Laboratory: